I spoke to an owner of a ON3 TT kit. He said the install was a pain, but the results were well worth it. That is pretty much what all the guys say. Bang for your buck. Just need someone who is good with fabrication and have some patience.
The customer support is hit and miss. I have personally had excellent customer service from Chad. My kit came with a wastegate that wasn't seating. After explaining why the issue was such an issue for me (took time off of work, needed the part to finish), he next day aired me one and it was in my hand 22 hours after I made the call.
The install and instructions are brutal, but no fab was required (most don't).